Antibodies have long been used in medical diagnosis, e.g., determining blood types, and in biological experimentation. The usefulness of antibodies, however, has been somewhat limited, as their complexity and diversity have made it very difficult to obtain homogeneous antibodies. Antibodies are complex protein or protein-based molecules which are produced by the immune systems of animals to protect the animal against foreign substances. Antibodies for medical use are generally obtained by injecting an animal with a foreign substance which will stimulate the animal's immune system and, most commonly, isolating an antibody fraction from the peripheral blood serum or from the ascitic fluid. The antibody fraction contains antibodies specific to the injected foreign substance as well as various other antibodies produced by the animal, and by known techniques, it may be possible to substantially isolate an antibody specific to the particular foreign substance. However, even when an antibody for a particular foreign substance is isolated, such antibody is actually a mixture of several antibodies which recognize various antigenic determinants of the foreign substance or related substances. While some individual antibody molecules may be highly specific, recognizing only a certain foreign substance or portion thereof, other antibody molecules may be less selective, recognizing not only the subject foreign substance but other substances as well. Because it is generally practically impossible to separate all related antibodies, even the most carefully purified antibody fractions may react with more than one substance.
In recent years, techniques of producing monoclonal antibodies have been developed which make it possible to obtain homogenous, highly specific antibodies. Generally, such antibodies are produced by immunizing an animal with a protein fraction or other foreign substance, obtaining antibody-producing cells from the animal, and fusing the antibody-producing cells with strains of myeloma cells, e.g., tumor cells, to produce hybridomas which are isolated and cultured as monoclones. The monoclonal hybridomas may either be cultured in vitro or may be grown as tumors in a host animal. Because each antibody-producing cell produces a single unique antibody, the monoclonal cultures of hybridomas each produce a homogeneous antibody which may be obtained either from the culture medium of hybridoma cultures grown in vitro or from the cells, ascitic fluid, or serum of a tumor-bearing host animal.
Not all of the hybridoma clones which result from fusing neoplastic cells with antibody-producing cells are specific for the desired foreign substance or antigen (a substance with which the antibody reacts) because many of the hybridomas will make antibodies which the inoculated animal has produced to react with other foreign substances. Even antibodies against the subject antigen will differ from clone to clone because antibodies produced by different cells may react with different antigenic determinants of the same molecule. From each clone, therefore, it is necessary to obtain the resulting antibody or the antibody-containing medium, serum or ascitic fluid and test its reactivity with the subject antigen and to test its specificity by determining with what other substances, if any, it recognizes. While the necessity of characterizing the antibody of each clone adds to the complexity of producing monoclonal antibodies, the wide variety of homogeneous antibodies which may be obtained gives investigators a number of very precise tools to map the structure and development of somatic cells.
The availability of homogeneous, highly specific monoclonal antibodies dramatically increases the value of antibodies as a diagnostic, experimental and therapeutic tool. Use of monoclonal antibodies for tumor and virus detection has been described in U.S. Pat. Nos. 4,172,124 and 4,196,265.
Monoclonal antibodies are particularly suitable for studying the pathways and processes by which cells differentiate into different types of cells. The proteins and other macromolecules in cells which may be precisely detected by monoclonal antibodies may serve as important clues to the derivation of cell lines. This may be particularly important when undifferentiated cancer cells are detected in the body and where the treatment of the cancer is dependent on the type of tumor present. The morphology of undifferentiated lymphoma cells may closely resemble the morphology of carcinoma cells, but the accepted treatments of lymphomas and carcinomas differ substantially. Thus it is highly important that it be determined as quickly as possible whether a cancer cell line in a patient is a carcinoma or a lymphoma line. Where the identity of the tumor line is not apparent from its gross morphology, highly specific monoclonal antibodies may be used to classify cell lines by their molecular composition.